/*
 * Radiotap parser
 *
 * Copyright 2007		Andy Green <andy@warmcat.com>
 */

#include "radiotap.h"
#include "wifibroadcast.h"

/**
 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
 * 
 * @iterator: radiotap_iterator to initialize
 * 
 * @radiotap_header: radiotap header to parse
 * 
 * @max_length: total length we can parse into (eg, whole packet length)
 *
 * Returns: 0 or a negative error code if there is a problem.
 *
 * This function initializes an opaque iterator struct which can then
 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
 * argument which is present in the header.  It knows about extended
 * present headers and handles them.
 *
 * How to use:
 * 
 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
 * checking for a good 0 return code.  Then loop calling
 * __ieee80211_radiotap_iterator_next()... it returns either 0,
 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
 * The iterator's @this_arg member points to the start of the argument
 * associated with the current argument index that is present, which can be
 * found in the iterator's @this_arg_index member.  This arg index corresponds
 * to the IEEE80211_RADIOTAP_... defines.
 *
 * Radiotap header length:
 * You can find the CPU-endian total radiotap header length in
 * iterator->max_length after executing ieee80211_radiotap_iterator_init()
 * successfully.
 *
 * Example code:
 * See Documentation/networking/radiotap-headers.txt
 */



int ieee80211_radiotap_iterator_init(struct ieee80211_radiotap_iterator *iterator,
                                     struct ieee80211_radiotap_header *radiotap_header,
                                     int max_length) {


    /*
     * Linux only supports version 0 radiotap format
     */
    if (radiotap_header->it_version) {
        return -EINVAL;
    }


    /* 
     * Sanity check for allowed length and radiotap length field 
     */
    if (max_length < le16_to_cpu(radiotap_header->it_len)) {
        return -EINVAL;
    }


    iterator->rtheader = radiotap_header;
    iterator->max_length = le16_to_cpu(radiotap_header->it_len);
    iterator->arg_index = 0;
    iterator->bitmap_shifter = le32_to_cpu(radiotap_header->it_present);
    iterator->arg = (__u8 *)radiotap_header + sizeof(*radiotap_header);
    iterator->this_arg = 0;


    /*
     * Find payload start allowing for extended bitmap(s) 
     */
    if (unlikely(iterator->bitmap_shifter & (1 << IEEE80211_RADIOTAP_EXT))) {
        while (le32_to_cpu(*((__u32 *)iterator->arg)) & (1 << IEEE80211_RADIOTAP_EXT)) {
            iterator->arg += sizeof(__u32);

            /*
             * Check for insanity where the present bitmaps keep claiming to extend up to or even beyond the
             * stated radiotap header length
             */
            if (((ulong)iterator->arg - (ulong)iterator->rtheader) > iterator->max_length) {
                return -EINVAL;
            }
        }

        iterator->arg += sizeof(__u32);

        /*
         * No need to check again for blowing past stated radiotap header length, because 
         * ieee80211_radiotap_iterator_next checks it before it is dereferenced
         */
    }

    /* 
     * We are all initialized happily 
     */
    return 0;
}



/**
 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 * 
 * @iterator: radiotap_iterator to move to next arg (if any)
 *
 * Returns: 
 *               0 if there is an argument to handle
 * 
 *         -ENOENT if there are no more args 
 * 
 *         -EINVAL if there is something else wrong.
 *
 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
 * in @this_arg_index and sets @this_arg to point to the
 * payload for the field.  It takes care of alignment handling and extended
 * present fields.  @this_arg can be changed by the caller (eg,
 * incremented to move inside a compound argument like
 * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
 * little-endian format whatever the endianess of your CPU.
 */
int ieee80211_radiotap_iterator_next(struct ieee80211_radiotap_iterator *iterator) {

    /*
     * Small length lookup table for all radiotap types we heard of
     * starting from b0 in the bitmap, so we can walk the payload
     * area of the radiotap header
     *
     * There is a requirement to pad args, so that args
     * of a given length must begin at a boundary of that length
     * -- but note that compound args are allowed (eg, 2 x u16
     * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
     * a reliable indicator of alignment requirement.
     *
     * upper nybble: content alignment for arg
     * lower nybble: content length for arg
     */

    static const __u8 rt_sizes[] = {
        [IEEE80211_RADIOTAP_TSFT] = 0x88,
        [IEEE80211_RADIOTAP_FLAGS] = 0x11,
        [IEEE80211_RADIOTAP_RATE] = 0x11,
        [IEEE80211_RADIOTAP_CHANNEL] = 0x24,
        [IEEE80211_RADIOTAP_FHSS] = 0x22,
        [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
        [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
        [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
        [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
        [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
        [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
        [IEEE80211_RADIOTAP_ANTENNA] = 0x11,
        [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
        [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11

        /*
         * Add more here as they are defined in
         * include/net/ieee80211_radiotap.h
         */
    };



    /*
     * For every radiotap entry we can at
     * least skip (by knowing the length)...
     */
    while (iterator->arg_index < sizeof(rt_sizes)) {
        int hit = 0;
        int pad;


        if (!(iterator->bitmap_shifter & 1)) {
            // arg not present
            goto next_entry; 
        }



        /*
         * Arg is present, account for alignment padding
         * 
         *  8-bit args can be at any alignment
         * 16-bit args must start on 16-bit boundary
         * 32-bit args must start on 32-bit boundary
         * 64-bit args must start on 64-bit boundary
         *
         * Note that total arg size can differ from alignment of
         * elements inside arg, so we use upper nybble of length
         * table to base alignment on
         *
         * Also note: these alignments are ** relative to the
         * start of the radiotap header **. 
         * 
         * There is no guarantee that the radiotap header itself 
         * is aligned on any kind of boundary.
         */

        pad = (((ulong)iterator->arg) - ((ulong)iterator->rtheader)) & ((rt_sizes[iterator->arg_index] >> 4) - 1);

        if (pad) {
            iterator->arg += (rt_sizes[iterator->arg_index] >> 4) - pad;
        }

        /*
         * This is what we will return to user, but we need to
         * move on first so next call has something fresh to test
         */
        iterator->this_arg_index = iterator->arg_index;
        iterator->this_arg = iterator->arg;

        hit = 1;

        /* 
         * Internally move on the size of this arg 
         */
        iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;

        /*
         * Check for insanity where we are given a bitmap that claims to have more 
         * arg content than the length of the radiotap section.  
         * 
         * We will normally end up equalling this max_length on the last arg, never exceeding it.
         */

        if (((ulong)iterator->arg - (ulong)iterator->rtheader) > iterator->max_length) {
            return -EINVAL;
        }

    next_entry:
        iterator->arg_index++;

        if (unlikely((iterator->arg_index & 31) == 0)) {
            /* 
             * Completed current u32 bitmap 
             */
            if (iterator->bitmap_shifter & 1) {
                /* 
                 * b31 was set, there is more
                 * 
                 * Move to next u32 bitmap 
                 */
                iterator->bitmap_shifter = le32_to_cpu(*iterator->next_bitmap);
                iterator->next_bitmap++;
            } else {
                /* 
                 * No more bitmaps: end 
                 */
                iterator->arg_index = sizeof(rt_sizes);
            }
        } else { 
            /*
             * Just try the next bit 
             */
            iterator->bitmap_shifter >>= 1;
        }

        /* 
         * If we found a valid arg earlier, return it now 
         */
        if (hit) {
            return 0;
        }
    }


    /* 
     * We don't know how to handle any more args, we're done 
     */
    return -ENOENT;
}
